The charge carriers which can be created in semiconductor materials include electrons and holes. For a given semiconductor material, the more abundant charge carriers are identified as majority carriers and the less abundant carriers are known as minority carriers. Whether electrons or holes are the majority or minority carriers in any particular semiconductor material is typically a function of doping. Charge carrier generation and charge carrier recombination are the processes where mobile charge carriers are created and eliminated. For example, in a solar cell, the energy of an incident photon may create a charge carrier. Therefore, charge carrier lifetime is a key functional parameter of a semiconductor material. Minority carrier lifetime is defined as the average time it takes an excess minority carrier to recombine with a majority carrier. Therefore, it is important in many aspects of semiconductor processing and device fabrication to quickly, inexpensively and reasonably accurately determine the minority carrier lifetime of a semiconductor material.
Known techniques for determining minority carrier lifetime in a semiconductor material include the following: time resolved photoluminescence (TRPL), photoconductive decay (PCD), radio frequency quasi-steady-state photoconductance (RF-QSSPC), radio frequency transient photoconductance, infrared lifetime mapping with carrier density imaging (ILM/CDI) and microwave-detected photoconductance (MDP). The known techniques for determining minority carrier lifetime can, in certain instances, be expensive and difficult to implement. For example certain techniques rely upon relatively expensive laser light sources to stimulate the material under investigation. Some techniques are challenging to implement in a large scale production setting as well. Furthermore, known techniques for determining minority carrier lifetime may determine only the minority carrier lifetime of the surface region of a semiconductor material.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.